The present invention relates to a sputtering apparatus for forming a thin film of a predetermined material on a predetermined substrate by the use of ions which are emitted by a discharge under a reduced pressure.
A sputtering apparatus according to the prior art is constructed such that a cathode and a substrate electrode are mounted in an evacuated chamber acting as a ground shield, and there is mounted on that cathode a target which is made of such a material as is to be deposited on the substrate. The substrate to be formed with a thin film made of the target material is placed on that electrode surface plate of the substrate electrode, which is positioned to face the cathode. The substrate electrode is either grounded to the earth or connected through a power divider with a high-frequency power source. The latter is called the "bias sputtering method", which is suitable for forming a flat thin film on a substrate having rough surfaces. This bias sputtering method is disclosed in detail in Japanese Patent Laid-Open Publication No. 50-24079 and Japanese Patent Publication No. 51-22912, for example. However, since the sputtering operation by such sputtering apparatus has a low deposition rate, a sputtering apparatus including a permanent magnet in the cathode has been used so as to enhance the deposition rate. The cathode thus having the permanent magnet therein is called the "planar magnetron high rate cathode", which is disclosed in detail in Japanese Patent Publication No. 53-19319, for example. Both the cathode and the substrate electrode of the sputtering apparatus thus far described according to the prior art have been made of a non-magnetic material such as Al, Cu, stainless steel or an alloy containing Al, Cu or the like.
FIG. 1a is a schematic section showing one example of a sputtering apparatus. In an evacuated chamber 11, there are mounted a cathode 12 and a substrate electrode 13. Inside of the cathode 12, there is disposed a permanent magnet 20. A substrate 15 to be formed with a desired thin film is made of Si, for example, and is placed on the electrode surface plate 14 (which is made of a non-magnetic material according to the prior art) of the substrate electrode 13. A target 16 is made of such a material as is to form the thin film on the substrate 15, such as Al or SiO.sub.2. The cathode 12 and the substrate electrode 13 are cooled with water, and the cathode 12 itself is connected with a high-frequency power source 17. On the other hand, the substrate electrode 13 is also connected through a power divider 10 with the high-frequency power source 17.
One example of the deposition rate distribution of the thin film material on the electrode surface plate 14 in case the sputtering operation is carried out by the use of the sputtering apparatus thus far described is plotted as a curve 18 in FIG. 1b. According to this example, the ratio of the radius r.sub.1 of a region (which will be shortly referred to as a "uniform region"), in which the distribution of the thickness of the film formed on the substrate 15 is within .+-.10%, to the radius R of the electrode surface plate is 0.18 at the most so that the region, in which the thickness of the thin film formed is substantially uniform, is remarkably limited. In other words, the usable size of the substrate 15 is undesirably limited to a remarkable extent according to the prior art apparatus. Incidentally, more detailed description referring to FIGS. 1a and 1b will be made in connection with the embodiments of the present invention.
The following references are cited to show the state of the art: (i) Japanese Patent Publication No. 51-22912; (ii) Japanese Patent Publication No. 53-19319; and (iii) Japanese Patent Laid-Open Publication No. 50-24079.